1. Field
Example embodiments relate to semiconductor memory devices, and more particularly to sensing circuits and phase change memory devices including the same.
2. Description of the Related Art
Nonvolatile memory devices using resistance materials include a resistive random access memory (RRAM), a phase change random access memory (PRAM), and a magnetic random access memory (MRAM). Dynamic random access memory (DRAM) and flash memory devices store data using charges. Nonvolatile memory devices using resistance materials store data using the resistance of variable resistive elements (e.g., RRAM), phase change of phase change material such as chalcogenide alloy (e.g., PRAM), and resistance change of magnetic tunnel junction (MJT) thin films according to the magnetization state of a ferromagnetice substance.
Using phase change memory cells as an example, the phase change material changes into a crystalline state or an amorphous state by cooling after heating. Since the phase change material in the crystalline state has a low resistance and the phase change material in the amorphous state has a high resistance, the crystalline state may be defined as set data (0), and the amorphous state may be defined as reset data (1).
The phase change material has a resistance characteristic that drifts as time elapses after date is written in memory cells. Therefore, in the phase change memory devices, it is difficult for data to be read right after the date is written in memory cells. In addition, a sensing margin is greatly influenced by stored data pattern.